A few of our users would like mail to be sent to their alias email address. From within the domain mail flow to the alias account works well, but from outside email accounts the emails get a failed delivery bounce back. I'm not sure what's wrong with the setup. I'm using exchange 2010. Please help.

We do have a 3rd party spam filter. I'm sure that's it. I just never think about that.

Thanks a lot!

Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the recipient domain. We recommend contacting the other email provider for further information about the cause of this error. The error that the other server returned was: 554 554 no valid recipients, bye (state 14).